This vacuum thing goes round and round, doesn't it?

I just pulled the spec sheet for my Chevy crate motor, a Fast-burn 385.
Set spark timing at 32 degrees BTDC at 4000 RPM with the vacuum advance line to the distributor disconnected and plugged. This setting will produce 32 degrees of total advance at WOT. The HEI vacuum advance canister should be connected to a ported vacuum source (no vacuum at idle).
Also, check this article:

http://chevyhiperformance.com/howto/97438/

Which, in part, says this:
Vacuum canisters advance according to engine vacuum, which is why they must be connected to a ported vacuum source. Ported vacuum is drawn from just above the throttle blades to make sure the vacuum canister does not advance at idle.
The vacuum advance on HEI distributors is meant to control part-throttle timing, not initial or WOT timing. As you come off idle, you get max ported vacuum, and your engine timing jumps way up. As you go to WOT, ported vacuum (and vacuum advance) drops off as mechanical advance comes in. At WOT, you have full mechanical advance and no vacuum advance. That's the way the advance curves are designed.

Can you hook the distibutor to manifold vacuum? Sure, but the timing curves go wacky.

Is this true for ALL HEI distributors? I honestly don't know - but for most of them out there today, it is.